(not applicable)
The invention relates generally to a combination quadrifilar and linearly polarized antenna, and more particularly to a combination linearly polarized and quadrifilar antenna able to provide excellent performance for both antennas in a low profile arrangement.
Charles D. McCarrick describes a combination monopole/quadrifilar helix antenna for S-band/Satellite applications on page 330 of the May 2001 edition of the Microwave Journal. FIG. 1 illustrates the monopole/ quadrifilar antenna 10 discussed in the McCarrick article. The antenna 10 includes a monopole 15 whose reflective element is a quarter-wave choke 14. Elements 14 and 15 form dipole antenna 13. The antenna 10 comprises a coaxial line 12 with a section of the outer conductor removed to expose the center conductor 15. The quarter-wave choke 14 is placed within a quadrifilar helix antenna shell 16 in an axially concentric fashion. The quadrifilar helix antenna is typically phased to produce circular polarization. Appropriate placement of the dipole antenna 14 within the quadrifilar antenna is critical for avoiding coupling between the two antennas and avoiding degradation of radiation patterns.
A combined antenna as described above has the disadvantages of having strict design requirements in terms of relative placement between antennas to avoid interference between the antennas and further requires a wider overall structure that may not necessarily be aesthetically pleasing. It is very difficult to optimize due to interactions between the dipole and quadrifilar helix. Furthermore, it is a mechanically-challenging structure and difficult to manufacture. The typical placement for such a combined antenna would be on the sloping back windshield of a vehicle. In this instance, for good satellite reception, care must be taken to ensure that most of the quadrifilar antenna xe2x80x9cclearsxe2x80x9d the line of sight with the transmitting satellite that may be blocked by the roof of the vehicle.
A combination linearly polarized/quadrifilar helix antenna 40 is illustrated in FIG. 2 as described in an application filed Jun. 6, 2001 and having application Ser. No. 09/875,728, now U.S. Pat. No. 6,483,47 which is incorporated by reference and assigned to the Assignee herein. It consists of a tubular dipole antenna 44 that is placed coaxially underneath the quadrifilar helix, but it should be noted that other types of dipole antennas, patches, or loop antennas (being linearly polarized) could easily replace the tubular dipole antenna. A (first) coaxial cable 46 is passed through the new tubular dipole with minimum effect on its performance. That coaxial cable 46 is connected to a feed network 48 of the quadrifilar helix antenna 49 and to a ground plane (residing behind the feed network 48-not shown) of the quadrifilar helix antenna 49. It should be noted that feed network 48 and quadrifilar shell 47 form the quadrifilar helix antenna 49. A (second) coaxial cable 42 preferably couples to a quarter wave hollow metal tube coupled to an inner conductor of coaxial cable 42 forming the tubular dipole antenna 44. The outer conductor of cable 42 (shield) is physically connected to the outer conductor (shield) of cable 46 and both are also connected to the shorted top section of tube 45. This configuration results in excellent performance for both antennas. Coaxial cable 46 has a minimum effect on dipole 44 due to the dipoles tubular structure. Also, this configuration results in minimum interaction between quadrifilar antenna 49 and dipole 44, but note that the dipole uses a separate tube to serve as a ground plane for the dipole antenna. Although helix antenna 40 does provide excellent performance and is simpler to construct than the antenna of FIG. 1, the quadrifilar antenna and the linearly polarized antenna of the combination do not share the same RF ground plane and is not fully integrated on a flexible substrate to provide further ease of assembly.
Thus, a need exists for a combined linearly polarized and quadrifilar antenna that will enable designers further freedom in the relative placement of the antennas while avoiding the detriments of coupling and interference between the antennas and further provide ease of assembly. Further, a need exists for a combined antenna that is esthetically pleasing that will be formed in a manner sharing a common ground plane.
In a first aspect of the present invention, a combination linearly polarized antenna and quadrifilar helix antenna comprises a flexible substrate, a quadrifilar antenna with a feed network etched on a first portion of the flexible substrate, an antenna with linear polarization etched on a second portion of the flexible substrate and a ground plane for the quadrifilar antenna and the antenna with linear polarization etched on the flexible substrate.
In a second aspect of the present invention, a combination monopole and quadrifilar helix antenna comprises a quadrifilar antenna having a feed network and a monopole antenna arranged below the quadrifilar antenna, wherein the monopole and the feed network share a common ground plane and wherein the monopole is at least partially below the common ground plane.
In a third aspect of the present invention, a method of manufacturing a combination monopole and quadrifilar antenna comprises the steps of forming a quadrifilar antenna pattern with a feed network on at least a first plane of a flexible substrate, forming a monopole antenna pattern on at least the first plane of the flexible substrate, and forming a ground plane pattern on at least a substantial portion of a second plane of the flexible substrate.